The present invention relates to a single crystal growing apparatus for compound semiconductor material of III-V, II-VI groups including gallium arsenide (GaAs), and more particularly to a single crystal growing apparatus of vertical gradient freezing method for compound semiconductor which is capable of obtaining rapid high temperature heating and uniform temperature distribution by utilizing a direct monitoring furnace as a higher temperature part furnace having double quartz tube applied with gold film in growing single crystal by utilizing vertical temperature gradient freeze method, and also capable of observing entire processes of single crystal growing directly with the naked eye.
Presently, horizontal Bridgman method and liquid encapsulated Czochralski method are widely known for typical two manufacturing methods which are being practically used in manufacturing gallium arsenide (GaAs) as a single crystal growing method which is being used generally.
Horizontal Bridgman single crystal growing method is a form in which liquid phase gallium and solid phase arsenic are respectively placed into the interior of quartz reaction tube provided with higher temperature part and lower temperature part and then, in a state that they are heated at high temperature and gallium arsenide (GaAs) is synthesized whereby molten gallium arsenide is obtained, while growing furnace around said quartz reaction tube is horizontally moved, then single crystal is grown. The wafer manufactured by such a single crystal growing method has advantage of maintaining high grade being less in dislocation density according to the lower temperature gradient, but on the contrary, cross section of the wafer is semicircle which is not a circle and its diameter is smaller, and therefore there has been disadvantage that manufacturing of the wafer having larger diameter more than 2 inches is difficult.
On the other hand, the wafer manufactured by liquid encapsulated Czochralski method is circular form in its cross section and having a relatively larger diameter more than 3 inches in its magnitude, on the contrary, since excessive thermal stress causing from high temperature gradient of axial or radial direction of solid-liquid interface is applied in the time of crystal growing, there has been a problem that larger dislocation density (10.sup.4 -10.sup.5 cm.sup.-2) is produced relative to the wafer manufactured through the horizontal Bridgman method.
Vertical gradient freeze method has been proposed as a single crystal growing method of new form developed by considering various problems encountered in such horizontal Bridgman method and liquid encapsulated Czochralski method.
Basic principle of the single crystal growing by this vertical gradient freeze method relates to a method that firstly gallium arsenide polycrystalline of high purity which is previously synthesized is filled into the interior of PBN (pyrolytic boron nitride) reaction container or quartz reaction container whereby it is fixed to the interior of a higher temperature part furnace and simultaneously arsenic for maintaining the interior of reaction tube to one atmospheric pressure is placed to a lower temperature part and thereafter temperature gradient of higher part is changed and thereby said polycrystalline is slowly solidified so as the solid-liquid interface is gradually moved to upward portion from starting point of seed crystal located at the bottom end portion of reaction container containing molten gallium arsenide by changing the temperature gradient of the higher temperature part so that single crystal is grown. After this method is tried for the growing of phosphide (GaP) single crystal firstly by S. E. Blum et al in 1973 [Refer to: S. E. Blum and R. J. Chicotka, J. Electrochem, Soc. 120(1973) 588], many researches have been carried out for this method.
As a single crystal growing apparatus of compound semiconductor of III-V group, II-IV group utilizing such a vertical gradient freeze method, a single crystal growing apparatus of semiconductor compound capable of manufacturing circular gallium arsenide wafer of larger diameter while exhibiting relatively lower dislocation density of semi-insulation property is described in U.S. Pat. No. 4,404,172.
However, the apparatus utilizing existing vertical gradient freeze method including aforementioned U.S. Pat. No. 4,404,172 use almost high pressure container, accordingly structure is complicated, and since not only difficulty is involved in manufacturing but also heat capacity of higher temperature part furnace is larger, sensitive temperature gradient can not be given in the time of single crystal growing, and in case that heating element is graphite heater, the temperature distribution around reaction tube is determined in accordance with the shape of said heater, so that it is not easy to find out while controlling voluntarily optimum crystal growing condition, and since the temperature control is executed on the basis of temperature measured by mounting a number of thermocouples, there is problem that single crystal growing process within the interior of furnace upon crystal growing can not be observed practically, and therefore there is disadvantage accompanying with difficulty for the crystal growing having reproducibility.